The invention relates to improvements in solid bowl worm centrifuges for the continuous separation of slurries containing substances differing in density and for separating the slurries into a light phase fraction and a heavy phase fraction.
More particularly, the invention relates to providing an improved solid bowl worm centrifuge which has a basket shell having a cylindrical portion at one end which receives and discharges the light phase and a conically tapering portion at the other end for discharging the heavy phase fraction. Discharge openings are provided in the first end for the light phase and discharge openings are provided in the conical end for the heavy phase. The bowl is driven in rotation and an auger is located therein independently driven in rotation.
A solid bowl worm centrifuge which has radial discharge nozzles for the heavy phase in the basket shell has been known and in such structure, the nozzle apertures projecting into the inside of the centrifuge are periodically opened and closed by a control element. The control element moves across the openings a short distance and is provided with release openings which are periodically opened and closed based on the measure of differential speed between the nozzle apertures and control element. These nozzle apertures are located at the beginning of the short steep conical part of the drum where the especially coarse solids are discharged.
In such a known solid bowl worm centrifuge which includes a nozzle discharge, one difficulty encountered is that the nozzle cross-sections allow only a limited quantity of solids per unit of time. An adaptation of this quantity on the basis of changing intake conditions during operation is not practically possible.
As a consequence thereof, a change or adjustment can be achieved only when the machine is shut down and brought to a standstill so that the nozzles can be replaced or the control element can be changed.
Further, only nozzles having a relatively small bore diameter can be employed and, for example, such diameters range between 3 and 10 mm. This is to be attributed to the fact that high static pressures are present in the heavy phase as a consequence of the high centrifugal acceleration at the nozzle aperture. With larger diameters, a plug of heavy phase could shoot through the nozzles at the time of opening and cause a flow collapse of the light phase situated above. This must be avoided under all circumstances, and therefore compels the provision of very small nozzle diameters.
It is accordingly an object of the present invention to provide a centrifuge wherein a matching of the withdrawable quantity of heavy phase due to changing intake conditions during ongoing operation is possible within a reasonable range of control.
A further object of the invention is to provide an improved centrifuge wherein the ratio of light phase material to the heavy phase material withdrawn is maintained relatively constant with a change in input to the separator due to changing intake conditions during ongoing operation.